This invention relates to a bandwidth switching circuit of an intermediate frequency or a high frequency amplifying circuit of a radio receiver, and more particularly a bandwidth switching circuit in which the switching is effected between differing signal paths having different pass bandwidths.
In a bandwidth switching circuit of the type referred to above, buffer amplifiers are provided for input and output parts of respective systems of a plurality of signal paths for preventing mutual interference and the amplifiers of the paths are not suitably ON.OFF-controlled so as to switch signals.
With such switching circuit, since amplifiers are provided on the input and output parts of the signal paths it is necessary to use a number of component parts for effecting switching thereby complicating the construction of the circuit. Moreover, as the amplifiers are connected in the signal paths it is necessary to use elements capable of operating at high frequencies for constituting the amplifiers, which also increases the cost of the tuner.
As above described buffer amplifiers are used for the purpose of preventing mutual interference between signal paths but since such amplifiers require a number of component parts, the buffer amplifiers can not operate effectively unless the component parts are efficiently arranged especially in view of shielding between the respective signal paths. When amplifiers are connected in respective signal paths it is necessary to adjust the amplifiers such that the gains of respective signal paths will be the same.